1. Field of the Invention
This invention relates to an adsorption type heat exchanger utilizing for cooling operation the coolant adsorbing and desorbing functions of a solid adsorbent, a method of controlling the cold output of the same cooler, and a fin type adsorbent heat exchanger used for the same cooler. More particularly, the invention concerns an adsorption type cooler, which has high COP (coefficient of product), can suppress variations of the adsorption efficiency of adsorbent and can provide stable cold blast for long time.
2. Prior Art
Adsorption type coolers which utilize the coolant adsorbing/desorbing function of a solid adsorbent for cold generation or heat pump operation, have many advantages such as the capability of effectively utilizing low class heat sources (at 50 to 850 c), for instance plant waste heat, hot water obtainable with solar heat collectors or the like, etc. and also less movable parts of compressors and the like, low equipment cost, less operating noise, etc. compared to compressor type coolers.
This type of adsorption type cooler usually uses water, alcohol, etc. as coolant, and employs a plurality of juxtaposed adsorbent heat exchangers accommodating a solid adsorbent, such as silica gel, zeolite, active carbon, active alumina, etc. In operation, adsorption and desorption of the coolant to and from the adsorbent are caused repeatedly while supplying the low class heat source for regeneration and the cooling water alternately to the heat exchanger. Thus, the evaporation latent heat of the coolant is utilized to obtain cold load output.
FIG. 8 shows the structure of an adsorption type cooler, to which the invention is applied. This cooler comprises two adsorbent heat exchangers 1 and 2 accommodating a solid adsorbent, a condenser 7 coupled to the heat exchangers 1 and 2 via respective vapor discharge valves 3 and 4, an evaporator (or coolant tank) 9 coupled to the heat exchangers I and 2 via respective vapor suction valves 5 and 6, a load water duct line HI for outputting cold water while heat exchange with coolant is carried out in the evaporator 9, a cooling water supply duct line B for supplying cooling water for adsorbing coolant, having been evaporated through heat exchange with load water in the evaporator 9, to heat exchange tubes in the heat exchangers I and 2, a cooling water return duct line E for draining heat-absorbed cooling water having been passed through one of the adsorbent heat exchangers I and 2 to the outlet side, a heat source water supply duct line C for supplying regeneration heat source water to the heat exchange tube of the other one of the heat exchangers I and 2 that has sufficiently adsorbed coolant to cause the coolant to be evaporated and desorbed from the adsorbent, a heat source water return duct line D for draining the heat source water heat robbed through the desorption to the outlet side, and a condensing cooling water duct line A for heat robbing and condensing evaporated coolant having been evaporated in the desorbing operation noted above and led into the condenser 7 through the vapor discharge valves 3 and 4.
The adsorbent heat exchangers 1 and 2 are housed in a vacuum housing 33 and isolated from each other by a partitioning wall 34, and they are capable of normal temperature evaporation of the coolant which is constituted by alcohol and water. The same structure and principles apply to the case where three or more adsorbent heat exchangers are employed.
The cooling water supply duct line B is branched from the 2 condensing cooling water duct line A, which is coupled via a pump 23 to the heat exchange tube 8 in the condenser 7 and thence to the downstream side of the cooling water return duct line E.
Designated at 15 is an inlet valve assembly comprising four valves for switching supply duct lines. That is, the valve assembly is used to switch the cooling water supply duct line B and the heat source water supply duct line C to bring about an adsorbing and a desorbing process of the adsorbent heat exchangers I and 2 alternately.
Designated at 19 is an outlet valve assembly comprising four valves for switching return duct lines. That is, like the above inlet valve assembly, this value assembly is used to switch the cooling water return duct line E and the heat source water return line D to corresponding ones of the adsorbent heat exchangers I and 2.
Designated at 13 is a coolant duct line extending between the condenser 7 and the evaporator 9. Through this duct line 13, condensed, i.e., liquid, coolant which has been obtained through heat robbing with cooling water in the condenser 7, is led via a valve 14 to the evaporator 9.
Designated at 10 is a coolant re-circulating duct line for leading liquid coolant stored in the evaporator 9 to a scatterer 12b to heat rob load water supplied to the heat exchange tube 12a in the evaporator 9 with latent heat of evaporation in FIG. 3.
Designated at 24, 29 and 11 are fluid pumps provided on respectively associated fluid duct lines, and at 25 is an on-off valve provided on the associated fluid duct line.
In this technique, when using the heat exchanger 1 for the adsorbing process and the other heat exchanger 2 for the desorbing process, the valves 15a and 15d of the inlet valve assembly 15 are opened while closing the other valves 15b and 15c thereof, and the valves 19c and 19b of the return duct line side outlet valve assembly 19 are opened while closing the other valves 19a and 19d thereof. Further, of the vapor suction valves 5 and 6 only the one on the side of the heat exchanger I in the adsorbing process is opened, and of the vapor discharge valves 3 and 4 only the one on the side of the heat exchanger 2 in the desorbing process is closed.
As a result, evaporated coolant obtained as a result of cooling and heat robbing by load water in the evaporator 9, is led through the vapor suction valve 5 into the heat exchanger 1 in the adsorbing process. At this time, cooling water is supplied through the valve 25, pump 24 and valve 15a to the heat exchanger 1, and thus the evaporated coolant is adsorbed to the adsorbent in the heat exchanger 1. The cooling water that has been heated through the adsorption is drained through the valve 19c to the outside.
Meanwhile, in the other heat exchanger 2 in the desorbing process, heat source water is supplied through the pump 26 and valve 15d to the heat exchanger 2, and coolant having been adsorbed to the adsorbent is desorbed and evaporated to be led through the vapor discharge valve 4 to the condenser 7.
In the condenser 7 which the condensing cooling water duct line A makes the cooling water supply duct line B branch, the evaporated coolant noted above is condensed by condensing cooling water led through the pump 23 to the heat exchange tube 8 in the condenser 7, the condensed, i.e., liquid, coolant being stored therein.
The liquid coolant thus stored in the condenser 7 is led through the coolant duct line 13 and valve 14 to the evaporator 9.
The liquid coolant led into the evaporator 9 is re-circulated through the coolant re-circulating duct line to be supplied through a scatterer to the heat exchange tube in the evaporator 9 to rob heat of load water, whereby cold output can be obtained from the load water duct line H leading from the evaporator 9.
After coolant has been sufficiently adsorbed to the adsorbent in the heat exchanger 1 in the adsorbing process, the valves 15a and 15d of the supply duct line side inlet valve assembly 15 are closed while opening the other valves 15b and 15c thereof, and the valves 19b and 19c of the return duct line side outlet valve assembly 19 are closed while opening the other valves 19a and 19d thereof. Further, the vapor suction valves 5 and 6 and vapor discharge valves 3 and 4 are switched.
As a result, the adsorbing and desorbing processes in the heat exchangers 1 and 2 are switched over to each other for the same adsorbing and desorbing operations as described above.
In the above adsorption type cooler which uses a solid adsorbent, unlike an absorption type cooler which uses.about.liquid absorber/wetter as absorbent and thus readily permits continuous control of the cold output (i.e., load) by varying absorbing and wetting conditions according to the circulation amount or temperature of the liquid absorber/wetter, once temperature conditions of the adsorption and desportion are determined, the coolant adsorption and desorption amounts in the heat exchangers I and 2 are determined absolutely by such conditions.
Besides, in one batch adsorbing cycle under a condition that a constant quantity of cooling water is circulated through the adsorbent heat exchangers 1 and 2, the adsorbing capacity of the adsorbent is not fixed; it is high right after the start of the cycle and reduced toward the end thereof. Therefore, unless the amount of adsorbed vapor is controlled to be constant during this time, the cold water outlet temperature is subject to variations.
Further, when a reduced capacity is required due to a change in load side utility condition, it is necessary to make adsorbing coolant vapor control in order to maintain the load water outlet temperature of the evaporator 9 at a predetermined constant temperature.
FIG. 9 shows changes in the evaporator inlet/outlet cooling water temperature in the operation of the above adsorption type cooler. As described before, right after the switching of the adsorbing and desorbing processes in a batch cycle, the adsorbing capacity of the adsorbent is high, and there is a tendency for coolant vapor adsorption from the evaporator 9 to match the state of the adsorbent at this time.
In the initial stage of the cycle time as shown at T1, T2, T3, . . . in FIG. 9, in which the coolant vapor adsorption amount is large, the evaporator inlet/outlet load water temperature is lower than predetermined temperature (which is, in this instance, 14 and 9'c of the load water at the inlet and outlet, respectively, of the evaporator 9).
With the progress of the adsorption, the adsorbing capacity is reduced, the cooling water outlet temperature rises gradually, and for last several minutes of the cycle time during which the capacity of the adsorbent approaches a limit, the capacity is higher than the preset value and near 14'c, the load water temperature at the inlet of the evaporator 9.
Such great difference of the adsorbing capacity of the adsorbent at the start and end of the batch cycle time, leads to variations of the load water at the outlet of the evaporator 9.
Further, even in an intermediate part of the batch cycle, a reduction of the load causes the cooling water to enter the evaporator 9 at a temperature below 14*c and leave the evaporator 9 at a temperature below 9*c.
For this reason, the prior art cooler as described above, which is subject to great cold water temperature variations, is usually used with a buffer water tank for uniformalizing the water temperature.
Even with this structure, however, when the cold water 6 provided on the outlet side the evaporator. The vapor suction valve is adapted to control the amount of coolant vapor supplied from the evaporator to the adsorbent heat exchanger in the adsorbing process according to the detected load cold water temperature.
With such a technique, it is possible to suppress load cold water temperature variations in the batch cycle through control of the flow rate of vapor to either adsorbent heat exchanger I or 2 in the adsorbing process according to the load cold water temperature. However, it is necessary to use an expensive controller for the flow rate control other than the vapor suction valve on-off operation thus increasing the overall cost.
Meanwhile, in the above adsorption type cooler, the adsorbent heat exchangers themselves have their own problem.
Specifically, the solid adsorbent is heated or cooled by cold or hot water in the heat exchange tube for heat exchange. However, unlike the heat exchange between usual fluids, heat transfer is effected through point contact between the solid (in many cases in the form of spheres) and the heat exchange tube and contact between solids. Therefore it is considerably difficult to improve the heat transfer efficiency, and a great deal of generating surfaces are necessary.
Meanwhile, where spaces enclosed by heat exchange tube are filled with adsorbent, the coolant vapor that is adsorbed or desorbed by the adsorbent has to pass through the interstices of the adsorbent and encounters resistance offered as it paSBeB. it is therefore difficult to obtain sufficient performance.
For this reason, the above heat exchange tube has, a structure as shown in Japanese Patent Laid-open Publication no. Sho 62-91763t in which circular fins made of aluminum or the like and having a specified height are provided at a predetermined pitch around the heat exchange tube through 9 which heat medium passes, the spaces defined between adjacent fins are filled with adsorbent, and each heat exchange tube is covered for the entire tube length with a metal net made from very thin wires to prevent detachment of the adsorbent.
This structure, however, has drawbacks that it requires a large number of heat exchange tubes to secure necessary amount of adsorbent meeting the capacity of the heat exchanger and also that the heat exchange tube arrangement including end tube support places to which the heat exchange tubes are secured is determined by also including a coolant vapor duct line to lead coolant vapor at the time of the adsorption and desorption thus increasing the size of the heat exchanger including all the heat exchange tubes.
Besides, in this type of adsorbent heat exchanger the heat exchange tubes are fabricated one after another, thus leading to cost increase.
To overcome this drawback, a structure as shown in FIG. 12 has been proposed. In this case, a plurality of horizontally extending heat exchange tubes 140 are disposed one above another. Also, a large number of plate-like aluminum fins 141 are fitted at a predetermined interval on the vertical array of the heat exchange tubes 140, and the spaces adjacent filled with granular adsorbent 142. To prevent the adsorbent 142 from being detached from the fin surface and inter-fin spaces and also movement of the adsorbent, the fin array is covered with a thin metal net 143 made of very thin wires (of about 40 meshes, for instance, although the mesh size depends on the grain size).
In this technique, however, the metal net of very thin wires which is used to cover the fins from the outer side for preventing the detachment of the adsorbent, is just like thin cloth and can not be held in close contact with the fins by itself. Therefore, it is necessary to hold the metal net from the outer side with coarse Mesh expand metals or the like to increase the close contact of the net.
However, even with such expand metals or the like it is considerably difficult to increase the close contact of the thin metal net uniformly over the entire surface of the filled adsorbent. Accordingly, such after-measure as making the expand metals locally taut are adopted to eliminate strain. However, this inevitably requires considerable man-hour.
Besides, the use of expand metals or like comparatively tough reinforcement to hold the metal net from the outer side, increases weight ineffective beat capacity and necessary heat when regenerating and cooling the adsorbent, thus deteriorating the COP.
Further, when the adsorbent heat exchanger in the prior art shown in FIG. 12 is required to have high capacity, it assembled by stacking a plurality of adsorbent heat exchangers of an increased size. However, the increased size adsorbent heat exchanger is subject to flexing of the metal net due to its own weight, thus resulting in detachment of the adsorbent from the fins or movement of the adsorbent.
In addition, when the element heat exchangers are raised or moved during assembling, local flexing of the metal net takes place to produce a gap between the metal net and the fin array, thus causing small particles of the adsorbent to fall down.
Moreover, since the prior art shown in FIG. 12 adopts the structure that the thin metal net is covered with the expand metals after covering the fin array with the metal net, the manufacture requires long time, substantial scale merits can not be obtained in view of the cost of manufacture and performance, and it is difficult to reduce cost and greatly improve performance.